Hypersensitivity

how many types of hypersensitivity are there?

4

what is meant by hypersensitivy

when the bodies immune system over reacts an harms the normal human cells

what is the main antibody responsible for type I hypersensitivity reactions

IgE

How fast do type 1 hypersensitivity reactions occor

very fast (within minutes)

what cells are involved in type 1 hypersensitivity reactions?

Mast cells, eosinophils, B cells and TH2 cells

what should be the normal function of the cells involved in type 1 hypersensitivy reactions?

to respond to invading parasites and kill them

why is the prevelence of type 1 hypersensitivity reactions increasing?

beacause the world is becoming more sterile, leading to a decreased ‘training’ of the immune system

How does exposure to parasites relate to the predisposition of an individual to develop an allergy

The more someone is exposed to parasites from a young age, the lower their chance of developing allergens is 

What happens upon the immune system first interaction with an allergen?

Th2 cells release cytokines causing more eosinophils to be produced and for B cells to switch classes to produce IgE antibodies 

How do mast cells and basophils bind to allergens

they express receptors which bind to Fc region of IgE antibodies

What occues on re-encounter of the allergen with the immune system

the allergens bind to IgE - coated mast cells and basophils, causing degranulation and release of vasoactive mediators. As well as expression of pro-inflammatory cytokines

What are vasocactive mediators 

hystamine and tryptase 

How can IgE mediatedallergic disorders be mediated 

avoidance of allergen, black mast cell activation, prevent mast cell activation, anti-inflammatory agents, adenaline immunotherapy

does immunotherapy always work

no

What are common mild symptoms to allergic reaction

Hives, excema, allergic rhinitis and asthma

What are severe symptoms to allergens

Increased vascular permeability and airway constriction leads to the inability to supply vital organs with oxygen

What does the release of histamine cause?

vasodilation, increased capillary permeability, smooth muscle contraction (closes bronchi)

What are the type ii hypersensitivity reactions mediated by?

IgM and IgG directed towards antigens present on cell surface

What are the 2 types of hypersensitivity reactions?

destruction of antigen-positive cells AND stimulation of cell surface antigens

Are type II hypersensitivities tissue specific?

Yes

What happens in the pathophysiology of a type II hypersensitivity reaction

Self-reactive B cells produce IgG and IgM. These antibodies then bind to normal human cells, destroying them

What results can arise from type II hypersensitivity reactions?

Phagocytosis of normal human cells and the onset of inflammation. Antibody can inhibit or stimulate cells to increase or decrease hormone release

What mediates type III hypersensitivity reactions

Soluble-immune complexes

What are the 2 parts of an immune complex

Antigen and antibody (Soluble)

What is the difference between type II and type III hypersensitivity reactions?

in type II, the antibody binds to an antigen on the surface of a cell. in type III, the antibody binds to a soluble antigen

How can type III hypersensitivity reactions be tracked?

The presence of pro-inflammatory complimentary proteins in the blood

What are type 4 hypersensitivity reactions driven by

CD4 + T cells

What occurs during type 4 hypersensitivity reactions

activation of CD4 + T cells leading to proliferation and macrophage recruitment/activation

What are classical hallmarks of a type 4

Large number of macrophages at reaction site, takes 24-48 hours for symptoms to occur

What is the general pathophysiology of type 4 hypersensitivity reactions?

sensitisation stage which produces Th1 cells that recognise an antigen